Two-seat XL1 brings vision of the
1-litre car close to production maturity

Wolfsburg / Doha, 25
January 2011 - Future mobility is one of the most stimulating topics
of our time. The key question here: Just how much could the energy
consumption of cars be reduced if all the stops were pulled out for
efficiency? There is now an answer to this question, and Volkswagen
is delivering it in the form of the new XL1. Combined fuel
consumption: 0.9 l/100 km. No other hybrid car powered by an
electric motor / internal combustion engine combination is more fuel
efficient. The prototype will be unveiled in a world debut at the
Qatar Motor Show (26 - 29 January).

To the point

Conceptually, the XL1
represents the third evolutionary stage of Volkswagen’s 1-litre car
strategy. When the new millennium was ushered in, Prof. Dr.
Ferdinand Piëch, who is today Chairman of the Supervisory Board of
Volkswagen AG, formulated the visionary goal of bringing to the
market a production car that was practical for everyday use with a
fuel consumption of 1.0 litre per 100 km. In the new XL1, Volkswagen
is demonstrating that this goal is now within reach.

The new Volkswagen XL1 attains a CO2 emissions value of 24 g/km,
thanks to a combination of lightweight construction (monocoque and
add-on parts made of carbon fibre), very low aerodynamic drag (Cd
0.186) and a plug-in hybrid system - consisting of a two cylinder
TDI engine (35 kW / 48 PS), E-motor (20 kW / 27 PS), 7-speed
dual-clutch transmission (DSG) and lithium-ion battery. The results:
with fuel consumption of 0.9 l/100 km, the new Volkswagen XL1 only
emits 24 g/km CO2. Since it is designed as a plug-in hybrid, the XL1
prototype can also be driven for up to 35 kilometres in pure
electric mode, i.e. with zero emissions at point of use. The battery
can be charged from a conventional household electric outlet.
Naturally, battery regeneration is also employed to recover energy
while slowing down and store as much of it as possible in the
battery for re-use. In this case, the electric motor acts as an
electric generator.

Despite the very high levels of efficiency, developers were able to
design a body layout that offers greater everyday practicality,
incorporating side by side seating rather than the tandem
arrangement seen in both the first 1-litre car presented in 2002 and
the L1 presented in 2009. In the new XL1, wing doors make it easier
to enter and exit the car. Further progress has been made by
manufacturing body parts from carbon fibre reinforced polymer parts
(CFRP), a technique used in Formula 1 car construction. Once again,
Volkswagen has successfully achieved significant reductions in
production costs– an important step forward to make viable a limited
production run of the XL1. Background: together with suppliers,
Volkswagen has developed and patented a new system for CFRP
production in what is known as the aRTM process (advanced Resin
Transfer Moulding).

II: The most efficient car in the
world

The new XL1 shows the
way forward for extreme economy vehicles and clean technologies. It
also demonstrates that such cars can also be fun. The feeling
when driving the XL1 is truly dynamic − not based on pure power,
rather on its pure efficiency. Two examples: 1) To travel at a
constant speed of 100 km/h, the prototype only needs 6.2 kW/8.4 PS –
a fraction of the performance of today’s cars (Golf 1.6 TDI with 77
kW and 7-speed DSG: 13.2 kW/17.9 PS). 2) In electric mode, the XL1
needs less than 0.1 kWh (82 Wh/km) to complete a one kilometre
driving course. These are record values.

When the full power of
the hybrid system is engaged, the Volkswagen prototype accelerates
from 0 to 100 km/h in just 11.9 seconds; its top speed is 160 km/h
(electronically limited). Yet these numbers alone do not tell the
whole story: Since the XL1 weighs just 795 kg, the drive system has
an easy job of propelling the car. When full power is needed, the
electric motor, which can deliver 100 Newton metres of torque from a
standstill, works as a booster to support the TDI engine (120 Newton
metres torque). Together, the TDI and E-motor deliver a maximum
torque of 140 Newton metres in boosting mode.

III: Plug-in hybrid concept

With the new XL1,
Volkswagen is implementing a plug-in hybrid concept, which utilises
the fuel efficient technology of the common rail turbodiesel (TDI)
and the dual clutch transmission (DSG). The TDI generates its stated
maximum power of 35 kW/48 PS from just 0.8 litre displacement. The
entire hybrid unit is housed above the vehicle’s driven rear axle.
The actual hybrid module with electric motor and clutch is
positioned between the TDI and the 7-speed DSG; this module was
integrated in the DSG transmission case in place of the usual
flywheel. The integrated lithium-ion battery supplies the E-motor
with energy. The high voltage energy flow from and to the battery or
E-motor is managed
by the power electronics, which operates at 220 Volts. The XL1’s
body electrical system is supplied with the necessary 12 Volts
through a DC/DC converter.

Interplay of E-motor and
TDI engine: The E-motor supports the TDI in acceleration (boosting),
but as described it can also power the XL1 prototype on its own for
a distance of up to 35 km. In this mode, the TDI is decoupled from
the drivetrain by disengaging a clutch, and it is shut down.
Meanwhile, the clutch on the gearbox side remains closed, so the DSG
is fully engaged with the electric motor. Important: The driver can
choose to drive the XL1 in pure electric mode (provided that the
battery is sufficiently charged). As soon as the electric mode
button on the instrument panel is pressed, the car is propelled
exclusively by electrical power. Restarting of the TDI is a very
smooth and comfortable
process: In what is known as “pulse starting” of the TDI engine
while driving, the electric motor’s rotor is sped up and is very
quickly coupled to the engine clutch. This accelerates the TDI to
the required speed and starts it. The entire process takes place
without any jolts, so the driver hardly notices the TDI engine
restarting.

When the XL1 is braked,
the E-motor operates as a generator that utilises the braking energy
to charge the battery (battery regeneration). In certain operating
conditions the load shared between the TDI engine and the electric
motor can be shifted so that the turbodiesel is operating at its
most favourable efficiency level. The gears of the automatically
shifting 7-speed DSG are also always selected with the aim of
minimising energy usage. The engine controller regulates all energy
flow and drive management tasks, taking into account the power
demanded at any given moment by the driver. Some of the parameters
used to realise the optimum propulsion mode for the given conditions
are:
accelerator pedal position and engine load, as well as the energy
supply and mix of kinetic and electrical energy at any given time.

Two-cylinder TDI uses
mass production technology: The 0.8 litre TDI (35 kW/48 PS) was
derived from the 1.6 litre TDI, which drives such cars as the Golf
and Passat. The 0.8 TDI exhibits the same data
as the 1.6-litre TDI common rail engine in terms of cylinder spacing
(88 mm), cylinder bore (79.5 mm) and stroke (80.5 mm). In addition,
the XL1’s two-cylinder and the mass produced four cylinder share key
internal engine features for reducing emissions. They include
special piston recesses for multiple injection and individual
orientation of the individual injection jets.

The excellent, smooth
running properties of the common rail engines were transferred to
the two cylinder engine. within addition, a balancer shaft that is
driven by the crankshaft turning at the same speed optimises smooth
engine running.

Meanwhile, the TDI’s
aluminium crankcase was constructed to achieve high rigidity and
precision, which in turn leads to very low friction losses. With the
goal of reducing emissions, exhaust gas recirculation and an
oxidation catalytic converter as well as a diesel particulate filter
are used. Equipped in this way, the 0.8 TDI already fulfils the
limits of the Euro-6 emissions standard.

Also designed for
efficiency is the vehicle’s cooling system. Engine management only
cools the TDI by activating an externally driven electric water pump
when engine operating conditions require it. This cooling system
includes an automatically controlled air intake system at the front
of the vehicle to reduce cooling system drag. This thermal
management strategy also contributes towards reduced fuel
consumption. A second electric water pump, which is also used only
as needed, circulates a separate lower temperature coolant loop to
cool the starter generator and power electronics.

IV: CFRP body is a technical
masterpiece

The development team
made extraordinary strides in designing the CFRP body − in terms of
its lightweight construction as well as its aerodynamics. A
comparison to the Golf illustrates just how innovative the body
concept of the new XL1 is:

The drag coefficient of
the highly successful Golf is very good for the compact class: Cd
(0.312) x A (frontal area 2.22 m2) equals a total drag figure of
0.693 m2 (Cd.A) providing this car with benchmark aerodynamic
credentials in its class. Meanwhile, the XL1 exceeds this
performance with a Cd value of 0.186 and a frontal area of 1.50 m2.
The product of these two parameters yields a total drag, or Cd.A
value of 0.277 m2 which is 2.5 times lower than that of the Golf.

Design for a new era:
The new XL1 is 3,888 mm long, 1,665 mm wide and just 1,156 mm tall.
These are extreme dimensions. The Polo has a similar length (3,970
mm) and width (1,682 m), but it is significantly taller (1,462 mm).
The height of the new XL1 is about the same as that of a Lamborghini
Gallardo Spyder (1,184 mm). So, it is easy to visualise just how
spectacular such a Volkswagen would appear on the road – as long and
wide as a Polo, but with a low profile like a Lamborghini.

The wing doors of the new XL1 are also reminiscent of a high-end
sports car. They are hinged at two points: low on the A-pillars and
just above the windscreen in the roof frame, so they do not just
swivel upwards, but slightly forwards as well. The doors also extend
far into the roof. When they are opened, they free up an
exceptionally large amount of entry and exit space.

Visually, the new XL1
also adopts the styling lines of the L1 presented in 2009; however,
the new prototype has a more dynamic appearance thanks to its
greater width. The design of the entire body was uncompromisingly
subjected to the laws of aerodynamics. In front, the new XL1
exhibits the greatest width; the car then narrows towards the rear.
Viewed from above, the form of the XL1 resembles that of a dolphin;
especially at the rear, where the lines optimally conform to the air
flow over the car body to reduce the Volkswagen’s aerodynamic drag.

In side profile, the
roofline reflects styling lines that trace an arc from the A-pillar
back to the rear. The rear wheels are fully covered to prevent air
turbulence; the air flows here are also optimised by small
spoilers in front of and behind the wheels. Observers will look for
door mirrors in vain; replacing them on the wing doors are small
cameras which take on the role of digital outside mirrors that send
images of the surroundings behind the car to two displays inside the
vehicle.

The front end of the new
XL1 no longer exhibits the typical radiator grille; however, it
still reflects the styling of the current Volkswagen “design DNA”
with a predominance of horizontal lines. Specifically, there is a
black cross-stripe (in the area where there is no longer a radiator
grille) that combines with the energy-efficient dual LED headlights
to form a continuous band. The actual air intake for cooling the TDI
engine, battery and interior is located in the lower front end
section and has electrically controlled louvres. The narrow turn
indicators are also designed in LED technology; these form an “L”
shape which vertically follows the wheel housing and horizontally a
line beneath the headlights. This creates a front end, which –
although it is completely redesigned and extreme in its dimensions –
can immediately be recognised as a Volkswagen design by its clean
lines.

At the rear, the design
takes an entirely new path, reinterpreting the brand values of
precision and quality. A new dimension of Volkswagen styling was
created here. Four characteristics are discernible:

1. Once again, the
dolphin body form that narrows towards the rear with very
precise trailing edges for perfect aerodynamics.
2. The coupé-shaped roofline without rear windscreen. Merging
into the roofline is the large rear boot lid that covers the
drive unit and 100 litre luggage space.
3. A strip of red LEDs that frames the rear section at the top
and on the sides. Integrated in this LED strip are the reversing
lights, rear lights, rear fog lights and brake lights.
4. A black diffuser, which exhibits nearly seamless transitions
to the completely covered underbody.

Lightweight
construction: more systematic than ever: Large sections of the new
XL1’s body consist of carbon fibre reinforced polymer (CFRP) − which
is as lightweight as it is strong. Specifically, the monocoque with
its slightly offset seats for driver and passenger and all exterior
body parts are made of CFRP. The layers of carbon fibre, which are
aligned with the directions of forces, are formed into parts with an
epoxy resin system in the aRTM process. This material mix produces
an extremely durable and lightweight composite. For a long time, it
was considered impossible to manufacture a body of CFRP, like that
of the new XL1, to industrial standards. Nonetheless, Volkswagen
successfully found a cost-effective way to mass produce CFRP parts
in sufficient volumes as early as 2009 – in the framework of the XL1
development project. Now this process has been further perfected.

CFRP is the ideal
material for the body of the new XL1 because of its light weight.
The XL1 prototype weighs only 795 kg. Of this figure, 227 kg
represents the entire drive unit, 153 kg the running gear, 80 kg the
equipment (including the two bucket seats) and 105 kg the electrical
system. That leaves 230 kg, which is precisely the weight of the
body – produced largely of CFRP − including wing doors, front
windscreen in thin-glass technology as in motorsport and the highly
safe monocoque. A total of 21.3 percent of the new XL1, or 169 kg,
consists of CFRP. In addition, Volkswagen uses lightweight metals
for 22.5 percent of all parts (179 kg). Only 23.2 percent (184 kg)
of the new XL1 is constructed from steel and iron materials. The
rest of its weight is distributed among various other polymers (e.g.
polycarbonate side windows), metals, natural fibres, process
materials and electronics.

Lightweight
construction: safer than ever: The new XL1 is not only lightweight,
but very safe as well. As mentioned, this is due in part to the use
of CFRP as a material. In the style of Formula 1 race cars, the
Volkswagen has a high-strength monocoque. In contrast to Formula 1,
however, this safety capsule is enclosed on top – for safety.
Depending on the type of collision, the load path may be directed
through the A- and B-pillars, cant rails and sills, all of which
absorb the impact energy. Additional side members and crossmembers
in the front and rear perfect the car’s passive safety.

V: Running gear with ESP utilises
high-tech materials

The running gear is
equipped with anti-roll bars at the front and rear and is
characterised by lightweight construction with maximum safety. In
front, a double wishbone suspension is used, while a semi-trailing
link system is employed at the rear. The front and rear suspension
are both very compact in construction and offer a high level of
driving comfort. The running gear components mount directly to the
CFRP monocoque in key areas.

Running gear weight has
been reduced by the use of aluminium parts (including suspension
components, brake calipers, dampers, steering gear housing), CFRP
(anti-roll bars), ceramics (brake discs) magnesium (wheels) and
plastics (steering wheel body). Friction-optimised wheel bearings
and drive shafts, as well as an entirely new generation of optimised
low rolling resistance tyres from MICHELIN (front: 115/80 R 15;
rear: 145/55 R 16), contribute to the low energy consumption of the
new XL1. Safety gains are realised by an anti-lock braking system
(ABS) and electronic stabilisation programme (ESP). That is because
sustainability without maximum safety would not really be a step
forward. The new XL1 shows how these two parameters can be brought
into harmony.